Recently, for the purpose of conservation of the global environment, in the field of motor vehicles, hybrid drive type motor vehicles have been sold by respective companies. Also, in the field of construction machines, for the purposes of reduction in fuel consumption and of reduction in CO2 emissions, hybrid drive type construction machines with engines and electric motors combined, and battery drive type construction machines which are driven by batteries only have been developed.
As for electrical storage devices for hybrid drive type construction machines, for example, capacitors or the like which can momentarily supply high power but have small electricity accumulation capacities may be used. Also, lead batteries, lithium ion batteries or the like which cannot momentarily supply high power but have large electricity accumulation capacities may be used. Further, both types of batteries may be used together. Generally, these electrical storage devices have low heat resistance temperatures and are often required to be sufficiently cooled by comparatively low temperature air. Particularly, the lead batteries have low heat resistance temperatures and are required to be sufficiently ventilated and cooled.
Moreover, these electrical storage devices are typically often heavy in weight and volumes required for mounting them are also often large. Therefore, as their installing places with respect to the vehicle bodies, examples which employ counterweight areas of rear end portions of vehicle bodies are disclosed in, for example, Patent Literature 1 and 2.
JP patent laid-open No. 2007-224585 as Patent Literature 1 discloses the following example. In a battery drive type construction machine, batteries are installed in a counterweight area that is provided in a rearmost portion of the construction machine and the batteries are cooled by a fan, and batteries that are heavy products are installed in the counterweight area so that the batteries also serve the role of a counterweight to achieve a weight balance between them and a boom.
However, according to the invention disclosed in Patent Literature 1, cooling air is not introduced directly from the outside air, but air after cooling an oil cooler is conducted to a fan for cooling the batteries in order to cool the batteries. In this cooling structure, the following cases become problems, such as, in a case where the number of installed batteries is large, in a case where the calorific values of the batteries are high, or in a case where the heat resistance temperatures of the batteries are low, the temperature of the cooling air supplied to the batteries rises compared to that of the outside air, thereby the cooling performance in the cooling of the batteries is deteriorated.
Moreover, JP patent laid-open No. 2003-328392 as Patent Literature 2 discloses an arranging structure for equipment of a hybrid drive type construction machine. This discloses a structure in which batteries are arranged in a counterweight area and covered with a cover. However, consideration is not paid to a structure for cooling the batteries themselves.
Therefore, in this installing structure for the batteries, the following cases become a problem, such as, in a case where the number of the installed batteries is large or in a case where the calorific values of the batteries are high, temperature of air around the batteries increases, thereby the cooling performance in the cooling of the batteries is considerably deteriorated.